1. Field of the Invention
The present invention relates to a cyclic conjugated diene copolymer. More particularly, the present invention is concerned with a cyclic conjugated diene copolymer comprising a main chain comprised of (A) cyclic conjugated diene monomer units, (B) monomer units obtained from vinyl aromatic monomers each having a hydrogen atom at the α-position thereof, and optionally (C) monomer units obtained from comonomers which are other than the monomers used for obtaining the monomer units A and B and which are copolymerizable with at least one of the monomers used for obtaining the monomer units A and B, wherein all monomer units A and the monomer units B together form one or more polymer chains each having an A/B random sequence, wherein the one or more polymer chains each having an A/B random sequence contain at least one polymer chain having a number average molecular weight of from 20,000 to 500,000 and contain no polymer chain having a number average molecular weight of more than 500,000. The present invention is also concerned with a hydrogenated, cyclic conjugated diene copolymer, a modified, hydrogenated, cyclic conjugated diene copolymer and a crosslinked, hydrogenated, cyclic conjugated diene copolymer which are obtained by subjecting the cyclic conjugated diene copolymers to a hydrogenation treatment, a hydrogenation/modification treatment and a hydrogenation/crosslinking treatment, respectively. The cyclic conjugated diene copolymer of the present invention has excellent properties with respect to heat resistance, transparency, nonhygroscopicity, chemical resistance and molding processability.
2. Prior Art
General-purpose polyolefins, such as polyethylene and polypropylene, have excellent chemical resistance, such as resistance to acids and bases, and have nonhygroscopicity. Further, general-purpose polyolefins (which are thermoplastic resins) have excellent recycling property and have a very high commercial value as a plastic, structural material. However, such general-purpose polyolefins cannot be used in application fields where high heat resistance and high transparency are required at the same time. For example, in the case of a general-purpose, crystalline polypropylene, the melting temperature thereof is only 170° C. at most, and the polypropylene has poor transparency. As a method for improving the heat resistance of general-purpose polyolefins, there can be mentioned a method in which the crystallinity of the polyolefin is increased. However, a general-purpose polyolefin having high crystallinity has poor transparency, as compared to that of a general-purpose polyolefin having low crystallinity. Thus, there has been a problem in that a general-purpose polyolefin cannot be used in application fields where high heat resistance and high transparency are required at the same time.
As an improved polyolefin, a cyclic polyolefin produced using a polycyclic norbornene monomer has been proposed (see Examined Japanese Patent Application Publication No. Hei 2-9612, Unexamined Japanese Patent Application Laid-Open Specification No. Sho 60-168708 and Examined Japanese Patent Application Publication No. Hei 8-26124). Such a cyclic polyolefin produced using a polycyclic norbornene monomer has a bulky 5-membered ring structure in the polymer main chain thereof and, therefore, the cyclic polyolefin has an amorphous structure having a softening temperature of about 160° C. and has a high commercial value as a material having excellent properties with respect to heat resistance and transparency, as compared to those of general-purpose polyolefins. However, the properties (heat resistance, stiffness, hardness and impact resistance) of such a cyclic polyolefin are not satisfactory in view of the high level properties which are required for transparent polyolefins in recent years.
As examples of improvements of a cyclic polyolefin produced using a polycyclic norbornene monomer, there can be mentioned cyclic olefin polymers produced by an anionic polymerization of 1,3-cyclohexadiene monomer (see U.S. Pat. Nos. 5,792,824, 5,795,945, 4,020,251 and 4,237,246). These cyclic olefin polymers which have a contiguous sequence of cyclohexane rings in the polymer main chain thereof, are advantageous not only in that these polymers have an amorphous structure having a softening temperature of more than 220° C., thereby realizing both high heat resistance and high transparency simultaneously, but also in that these polymers have high stiffness and high hardness. Further, in the case of these polymers, the impact resistance is greatly improved without sacrificing the heat resistance, by realizing a polymer block structure comprising a cyclohexane polymer block comprised of a contiguous sequence of cyclohexane rings and a rubber component polymer block comprised of butadiene monomer units or isoprene monomer units, wherein such polymer block structure is achieved utilizing the living polymer-forming property of the anionic polymerization used for producing these polymers.
However, due to the contiguous sequence of cyclohexane rings of the cyclic olefin polymers, the solvent which can dissolve these polymers is substantially limited to decahydronaphthalene which has a high boiling point, thus posing a problem in that, in the solvent cast method which is necessary for producing an optical film which is required to have a high level of properties, the removal of the solvent becomes very difficult, thus posing a big problem on the molding-processability. Also, due to the contiguous sequence of cyclohexane rings, the melt-molding temperature of the cyclic olefin polymers is very high, leading to a large difficulty in the melt-molding in commercial production of shaped articles.
For solving this problem, it has been attempted to effect a so-called randomization, i.e., to effect a random insertion of other monomer units into the contiguous sequence of cyclohexane rings so as to form a random copolymer chain. As an example of such randomization, it is known that recurring units obtained from a styrene monomer are randomly inserted into a polymer chain comprised of recurring units obtained from a cyclohexadiene monomer (see Polymer Preprints 2001, 42 (1), 436, and Synthetic Metals 102 (1999) 1211–1212). However, in such cases, although a randomization can be achieved, the random copolymer chain in the obtained cyclic olefin polymer has a disadvantage in that the number average molecular weight of the random copolymer chain is low, so that the cyclic olefin polymer cannot satisfy the high level properties, especially impact resistance at a high level, which are required for optical films in recent years.
Thus, conventionally, it has never been possible to obtain a cyclic olefin polymer which has excellent properties with respect not only to heat resistance, transparency, nonhygroscopicity and chemical resistance, but also to processability.